Tricks for getting him to go #2 in the potty??

My son is almost 8, but developmentally disabled, (think of him like a 2 1/2- 3 yr old)... So, since his las tbrain surgery I have FINALLY gotten him to go #1 in the potty!!! He is wearing big boy underpants, and putting ALL of his pee in there, as long as I take him at regular intervals throughout the day... If I put a pull-up on him he pees in it, so I have to keep him in underpants now so we don't lose all this amazing progress! But, he is pooping in his pants 1-2 times a day. He doesn't show any signs that he is going. It is NOT at regular times of the day. He doesn't seem to notice or care that there is poop in his pants, just keeps playing until I smell it. He has loose bowels so this is DISGUSTING and messy, AND he doesn't strain or give any sign that he is going... HELP!!! Any tricks to teach them to put it IN the toilet?? I'm having no success with poop, after a full month of potty training...

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